Toshiba MMY-MAP0806HT7(J)P, Service Manual

Page: 72 / 350

5. Oil
equation
control This control function is aimed at preventing compressors from running out of oil by
evening out the oil supply to outdoor units, and is basically performed by opening/
closing solenoid valves SV3A, SV3B, SV3C, SV3D.
There are three control patterns
as described below. (For a schematic diagram of oil equalization control, see page
57
.)
1. Preparatory control
If the oil level judgment result in the memory continues to be “low” for 30 seconds,
SV3B is turned on, with SV3D turned on and off intermittently.
• Oil accumulated in the oil
separator is returned to the
compressor.
2. Oil equation control
This control function is performed to transfer oil to the outdoor unit whose oil level is
low from other outdoor units. It takes place whenever the header unit registers a low
oil level result while at least one of its compressors is turned on or at least one of the
follower units issues an oil level equation request.
This control function does not apply to a header unit-only system (no follower units
connected).
• This is normal oil
equalization control.
3. Oil depletion protection control
This control function is performed if oil equation control fails to achieve an optimum
oil level. In concrete terms, if a low oil level situation continues for 30 minutes, the unit
is brought to a protective shutdown, followed by a restart 2 minutes and 30 seconds
later. If protective shutdown is repeated three times, the error is confirmed as final.
(There will be no more restarts.) The
check
code is “H07”.
• This protective control is
performed when a
prolonged low oil level is
detected.
6.
Refrigerant/
oil recovery
control 1. Cooling oil (refrigerant) recovery control
Performed during cooling, this control function aims to: periodically collect any
refrigerating oil condensate that has built up in inter-unit gas pipes and indoor units
and return it to outdoor units when the compressor operation command is
inadequate; and prevent the accumulation of refrigerant in outdoor heat exchangers
while cooling operation is in progress under low outside air temperature conditions.
It is managed by the header outdoor unit.
1) Control commencement conditions
• When cooling operation has continued for at least 2 hours
• When cooling operation has started (compressors have just been turned on, though
this does not always happen depending on outside air temperature conditions).
2) Control details
• All compressors currently in operation are operated at the minimum speed, with those
currently not in operation turned on.
• Indoor units are set to the cooling oil (refrigerant) recovery control mode, with their
indoor PMVs opened to a certain degree.
• Compressors are operated at the target speed.
• After recovery control is performed for a specified period of time, it is terminated, and
normal cooling operation resumes.
• Cooling oil recovery control
takes place approximately
every 2 hours.
• Control duration is about 2 to
5 minutes, though it varies
according to the operating
conditions of the system.
2. Heating refrigerant (oil) recovery control
Performed during heating, this control function aims to recover any liquid refrigerant
trapped inside indoor units that have been turned off. It also serves the additional
purposes of recovering indoor/outdoor refrigerant after defrosting and recovering oil
present in outdoor heat exchangers during heating overload operation.
This control function is managed by the header outdoor unit.
1) Control commencement conditions
• When heating operation has started (compressors have just been turned on)
• When heating takes over upon completion of defrosting
• When heating operation has continued for 60 minutes
2) Control details
• All compressors currently in operation are operated at the minimum speed, with those
currently not in operation turned on.
• Indoor units are set to the heating refrigerant (oil) recovery control mode, with their
indoor PMVs opened to a certain degree.
• Compressors are operated at the target speed.
• Upon completion of refrigerant recovery for all the indoor units, normal cooling
operation resumes.
• Heating oil recovery control
takes place approximately
every hour.
• Control duration is about 2 to
10 minutes, though it varies
according to loading
conditions.
• Compressor rotational
speed varies with control
conditions, indoor unit
capacity, and outdoor unit
specification.
Item Description of operation, numerical data, and other information Remarks
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